Hi,
I would be so bold as to suggest that if the tapes were on 7" reels and recorded on some tube-based consumer machine of the 50s era, the most likely format for them to be in is what is called "2 track" or "1/2 track" mono, containing 2 mono tracks, each covering half the width, where the reels were flipped at the end, and the tape was played or recorded on the other half till it was back on the reel it started from. So be sure and recover side 2 (if any) when you transfer. The 2 most common speeds were 7 1/2 and 3 3/4 inches per second. The good news is that these sorts of self contained, mono recorders were very common up through the end of the 1960s and would have been solid state on the later units.
As any of the machines are over 40 years old, as was pointed out, it is hard to find one in really reliable good working condition to transfer long hours of tape, which may be fairly fragile now, as was also pointed out. Capacitors and rubber drive belts and wheels slowly fail over time, tape heads wear, grease gets sticky, and of course things get dirty. But I have found machines of this era that are still working more or less as designed.
Most will have an external headphone monitor or speaker output, which typically is a mono mini jack or perhaps 1/4" jack. You might find one with an RCA "line out" jack. This would be preferable for a clean output to your computer's input. Sometimes the level can be an issue with some sound cards and USB devices. A volume control dependent external speaker out into a microphone input on the computer will probably yield a somewhat noisy and/or possibly overloaded, distorted level into the computer. A computer with stereo line in with the single mono output "Y"ed to L & R channels should work best. If it is speaker level there will be an optimum setting of the recorders volume control for level vs noise.
If you end up with a stereo deck, it can still work, but you will use only the left channel output, as the right channel will give you the other side of your tape playing backwards! This is due to the peculiar way stereo was done vs mono on reel to reel tape. If, BTW you play the tapes on a stereo deck and both channels yield normal output, it was recorded on a stereo deck, but not so likely in the 50s, especially with one big green "eye" meter. (very typically a Webcor or VM)
Not to be too discouraging, but a quick look at Craigslist in the SLO, Santa Barbara and Bakersfield areas did not yield anything that particularly looked suitable. Oh well...
A basic, school A/V type Wollensak, Sony TC-104 or 105 or Califone/Rheem might be a good place to start looking on eBay.
Make sure you do _not_ get a battery powered 5" reel mono machine. These are also very very common, but obviously will not play your 7" reels.
BTW, one meter and one set of inputs and outputs are your clues that it is not a stereo unit.